Touch screens based on materials that conduct electricity uniformly have been in use for several decades. One of the first touch screens was made from two sheets of conductive paper so arranged that two independent electrical fields ran orthogonal in a steady state (Hurst and Parks, U.S. Pat. No. 3,662,105). Later improvements consisted of using an array of highly conductive dots as electrodes around the rectangular perimeter and a complementary array of diode switches, or preferably a resistor network, such that only one conductive sheet was required. Potentials were then measured in a timed sequence (Hurst, U.S. Pat. No. 3,798,370) to obtain both an x and a y coordinate. This development, along with a conducting and transparent ‘cover sheet’ with radius of curvature discrimination (Hurst and Colwell, U.S. Pat. No. 3,911,215) helped pave the way to transparent touch screens that could be used on the computer terminal (Talmage et al, U.S. Pat. No. 4,071,689 and Gibson et al, U.S. Pat. No. 4,220,815).
When diode switches were replaced with voltage dividers using fixed resistors connected to a pattern of highly conducting dots, the switching required to sample the two time sequenced electrical fields was greatly simplified. This concept evolved into the use of a carefully designed frit pattern in order that equipotentials could be representative of Cartesian coordinates (Talmage et al, U.S. Pat. No. 4,797,514) even near the edges of the screen. Recently a bordered electrode design was introduced (Hurst, et al. U.S. Ser. No. 09/262,909, now U.S. Pat. No. 6,650,319, issued Nov. 18, 2003) to greatly simplify the production of touch screens. This design consists of a narrow border that encloses the working area and is made of a material that is intermediate in electrical conductivity between the highly conductive electrodes and that of the sensor coating.
The present disclosure relates to a touch screen whose rectangular area is enclosed with a border that is divided into a number of smaller rectangular areas using lines of specified width and electrical conductivity. With this technique the coating uniformity requirement is reduced. Essentially, uniformity requirements apply not to the entire area of the touch screen but to the smaller areas defined with the grid of conducting lines. With this innovation, the construction of large touch screens, even wall size or floor size, can be accomplished. This would make possible a number of new applications such as interaction with image projection equipment, input information for robots, position sensitive information for security, or inputs for virtual reality equipment.
With modern electronics technology, it is economically feasible to apply corrections to data from touchscreens with non-uniform fields to obtain accurate Cartesian coordinates. For example, Hurst, et al. U.S. Ser. No. 09/262,909 has shown that topological mapping can be advantageously used to build resistive touch screens with relaxed uniformity requirements much more economically, without the loss of performance. In this topological method equipotential pairs are mapped to a pair of Cartesian coordinates even under conditions where individual equipotentials do not map to give unique x and y coordinates. However, with some electrode geometry (for example a spot electrode at each corner of a rectangle) equipotential pair measurements on some regions of the sensor cannot be uniquely mapped to Cartesian coordinates. The use of the border concept provides unique pair mapping over the entire working area of the sensor, even very close to the edges.
The present invention provides a grid arrangement that makes more screen area available even without electronic data correction. However with extremely large screens which might be prepared with large individual sensing areas defined by grids, gross non-uniformity would be expected and, when necessary, electronic mapping may be applied.